Semiconductor processing wherein a substrate is processed in a process chamber can be particularly sensitive to process gas flow rate variations and perturbations. In particular, variations may affect one or more critical dimensions and/or film thicknesses during processing, for example. Thus, gas delivery assemblies for semiconductor processing chambers attempt to deliver steady flows at precise flow rates, flow ratios, and pressures to multiple input ports of a process chamber.
Prior art gas delivery assemblies may utilize flow-splitting methods to improve flow ratio accuracy, repeatability, and reproducibility in multi-injection point and, multi-chamber processing systems. Flow splitting can be provided by using a plurality of mass flow controllers (MFCs), which actively attempt to control the relative flow rates of gases dispensed at the multiple input port locations. However, as new chamber processing technologies continue to achieve smaller critical dimensions for microelectronic devices, even higher degrees of flow control precision, and in particular, flow ratio control, are beneficial. Therefore, methods and assemblies are desirable for making gas flow rate control, and in particular, flow ratio control, more precise.